Akka round-robin: Sending response from remote routees to sender

I am using Akka Cluster (version 2.4.10) with few nodes designated for "front-end" role and few others as "workers". The workers are on remote machines. The incoming work is distributed by the front-end actor to workers by round-robin routing. The issue is sending back the response from the "workers" back to the front-end actor. I can see that the work is getting completed by the workers. But the message sent by the workers to front-end does not reach and ends up as dead-letters. I see the below error in the log.

I have seen this and I am following the same in my code. I have also seen this, but the solution suggested does not apply in this case, because I do not know the routees up-front. It comes through the configuration and it can change. The round-robin router configuration is as below.